Testing devices for providing an indication of a circuit condition are many and varied in design. In complex systems that perform complex functions it is sometimes difficult to locate where the capabilities of certain of the components have gone awry. While conventional volt meters, amp meters or ohm meters help give an indication where a defect may be, these meters usually require considerable training to use them properly in a complex system and when the meters themselves become impaired, the indications they provide might be erroneous.
The modular approach for complex system design allows a more rapid testing of a large group of components on a circuit board; yet the savings in time are not without a price. Usually an elaborate and highly specialized test plug-in fixture is needed to enable the rapid testing of a complex module. When a number of slightly different modules are used in a sophisticated electronics system, the number of test fixtures must also be increased at a consequential greater cost, need for greater storage space and requirement for longer shelf life between activations and use. In addition, discarding an entire complex module because one small component may be inoperative might not be cost effective.
Thus, a continuing need exists in the state of the art for a test instrument that enables a spot by spot checking of a serial data stream in an electronics system that can localize a defective portion to allow its economical repair.